1. Field of the Invention
The present invention relates to an exchange biased self-pinned spin valve sensor with recessed overlaid leads and, more particularly, to such a sensor wherein first and second leads engage first and second recessed portions of a cap layer of the sensor so that resistance between the leads and the sensor is reduced.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has write and read heads, a suspension arm and an actuator arm. When the disk is not rotating the actuator arm locates the suspension arm so that the slider is parked on a ramp. When the disk rotates and the slider is positioned by the actuator arm and suspension arm above the disk, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the actuator arm swings the suspension arm to place the write and read heads over selected circular tracks on the rotating disk where field signals are written and read by the write and read heads. The write and read heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a spin valve sensor for sensing the magnetic field signals from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer structure and a ferromagnetic free layer structure. An antiferromagnetic pinning layer typically interfaces the pinned layer structure for pinning a magnetic moment of the pinned layer structure 90xc2x0 to the air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer structure is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from the rotating magnetic disk. The quiescent position, which is preferably parallel to the ABS, is the position of the magnetic moment of the free layer structure with the sense current conducted through the sensor in the absence of field signals.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layer structures are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layer structures. When the magnetic moments of the pinned and free layer structures are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos xcex8, where xcex8 is the angle between the magnetic moments of the pinned and free layer structures. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer structure rotates from a position parallel with respect to the magnetic moment of the pinned layer structure to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel.
In addition to the spin valve sensor the read head includes nonconductive nonmagnetic first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is formed first followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a bottom spin valve sensor or a top spin valve sensor depending upon whether the pinned layer is located near the bottom of the sensor close to the first read gap layer or near the top of the sensor close to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel (AP) pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic AP layers that are separated by a coupling layer with magnetic moments of the ferromagnetic AP layers being antiparallel to one another. Spin valve sensors are still further classified as single or dual wherein a single spin valve sensor employs only one pinned layer and a dual spin valve sensor employs two pinned layers with the free layer structure located therebetween.
As stated hereinabove, a magnetic moment of the aforementioned pinned layer structure is pinned 90xc2x0 to the ABS by the aforementioned antiferromagnetic (AFM) pinning layer. After deposition of the sensor layers the sensor is subjected to a temperature at or near a blocking temperature of the material of the pinning layer in the presence of a field which is oriented perpendicular to the ABS for the purpose of resetting the orientation of the magnetic spins of the pinning layer. The elevated temperature frees the magnetic spins of the pinning layer so that they align perpendicular to the ABS. This also aligns the magnetic moment of the pinned layer structure perpendicular to the ABS. When the read head is cooled to room temperature the magnetic spins of the pinning layer are fixed in the direction perpendicular to the ABS which pins the magnetic moment of the pinned layer structure perpendicular to the ABS. After resetting the pinning layer it is important that subsequent elevated temperatures and extraneous magnetic fields do not disturb the setting of the pinning layer. It is also desirable that the pinning layer be as thin as possible since it is located within the track width of the sensor and its thickness adds to an overall gap length between the first and second shield layers. It should be understood that the thinner the gap length the higher the linear read bit density of the read head. This means that more bits can be read per inch along the track of a rotating magnetic disk which enables an increase in the storage capacity of the magnetic disk drive.
A scheme for minimizing the aforementioned gap between the first and second shield layers is to provide a self-pinned AP pinned layer structure. The self-pinned AP pinned layer structure eliminates the need for the aforementioned pinning layer which permits the read gap to be reduced by 120 xc3x85 when the pinning layer is platinum manganese (PtMn). In the self-pinned AP pinned layer structure each AP pinned layer has an intrinsic uniaxial anisotropy field and a magnetostriction uniaxial anisotropy field. The intrinisic uniaxial anisotropy field is due to the intrinsic magnetization of the layer and the magneto striction uniaxial anisotropy field is a product of the magneto striction of the layer and stress within the layer. A positive magnetostriction of the layer and compressive stress therein results in a magnetostriction uniaxial anisotropy field that can support an intrinsic uniaxial anisotropy field. The orientations of the magnetic moments of the AP pinned layers are set by an external field. This is accomplished without the aforementioned elevated temperature which is required to free the magnetic spins of the pinning layer.
If the self-pinning of the AP pinned layer structure is not sufficient, unwanted extraneous fields can disturb the orientations of the magnetic moments of the AP pinned layers or, in a worst situation, could reverse their directions. Accordingly, there is a strong-felt need to maximize the uniaxial magnetostriction anisotropy field while maintaining a high magnetoresistive coefficient dr/R of the spin valve sensor.
It is also important that the free layer be longitudinally biased parallel to the ABS and parallel to the major planes of the thin film layers of the sensor in order to magnetically stabilize the free layer. This is typically accomplished by first and second hard bias magnetic layers which abut first and second side surfaces of the spin valve sensor. End portions of the free layer abutting the hard bias layers are over-biased and become very stiff in their response to field signals from the rotating magnetic disk. The stiffened end portions can take up a large portion of the total width of a sub-micron sensor and can significantly reduce the amplitude of the sensor. It should also be understood that a narrow track width is important for promoting the track width density of the read head. The more narrow the track width the greater the number of tracks that can be read per linear inch along a radius of the rotating magnetic disk. This enables a further increase in the magnetic storage capacity of the disk drive.
There is a need to reduce the total stack height of the read sensor without sacrificing the magnetoresistive coefficient dr/R. There is also a need to reduce the stiffening of the magnetic moment of the free layer when longitudinally biased and to minimize disturbance of the magnetic moments of the AP pinned layers.
An aspect of the invention is to employ an exchange biasing scheme for longitudinally biasing the free layer. This is accomplished by providing the free layer with first and second wing portions which extend laterally beyond the track width of the sensor and which interface first and second antiferromagnetic (AFM) biasing layer layers so as to implement an exchange bias therebetween. This arrangement will enhance the stabilization of the free layer and will result in the read head having a higher amplitude read output.
The spin valve sensor has a central portion which extends between the first and second AFM layers. An aspect of the invention is to provide first and second lead layers which overlay the first and second AFM layers respectively and further overlay first and second portions respectively of the central portion of the spin valve sensor so that a distance between the first and second lead layers defines a track width of the sensor that is less than a distance between the first and second AFM layers. With this arrangement uniform biasing of the free layer is promoted.
A spin valve sensor further includes a cap layer structure which typically includes a layer of tantalum (Ta). Another aspect of the invention is to provide the cap layer structure with a full thickness portion which is located between first and second reduced thickness portions with the first and second lead layers engaging the cap layer structure within the first and second reduced thickness portions. Since tantalum (Ta) has a high resistance the reduced thickness portions provide less resistance between the first and second lead layers and the sensor for conducting the sense current therethrough.
A further aspect of the invention is to provide a self-pinning antiparallel (AP) pinned layer structure without an AFM pinning layer pinning the AP pinned layer structure. The self-pinning is accomplished by providing the ferromagnetic AP pinned layers within the AP pinned layer structure with uniaxial anisotropies which are oriented perpendicular to the ABS and, in combination, self-pin the magnetic moments of the first and second AP pinned layers perpendicular to the ABS and antiparallel with respect to each other. Cobalt iron (CoFe) is preferably employed for each of the first and second AP pinned layers in a self-pinned AP pinned layer structure.
An object of the present invention is to provide a low stack height spin valve sensor with an exchange biased free layer, a self-pinned antiparallel (AP) pinned layer structure which has a high magnetoresistive coefficient dr/R, a uniformly biased free layer and a narrow track width.
Another object is to provide the aforementioned spin valve sensor wherein first and second lead layers engage first and second reduced thickness portions of a cap layer structure for reducing the resistance between the lead layers and the spin valve sensor.
A further object is to provide various methods of making the foregoing read heads.
Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings.